Apparatus for processing photographic films

ABSTRACT

A processing apparatus wherein a dryer follows a first vessel for a supply of developing solution, a second vessel for a fixing bath and a third vessel for a rinse bath. The duct for evacuation of spent gaseous fluid from the dryer contains a heat exchanger whose coil conveys a stream of fresh water which is heated in the coil prior to entering additional heat exchangers in the first two vessels. The additional heat exchangers heat the respective liquids and the last additional heat exchanger discharges heated water into the rinse bath. The vessel for developing solution further contains a thermostatically controlled heating unit. The heat exchanger in the dryer receives unheated water from a supply pipe through a valve which is opened in automatic response to admission of films into the first vessel and remains open as long as at least one film travels between the inlet of the first vessel and a receptacle which receives films from the dryer.

[451 Aug. 27,1974

3,349,688' 10/1967 Buechner....'.........,.................. 95/96 3,470,810 l0/l969 Buechner................. ............L. 95/95 3,613,547 l0/l97l 95/89 R Primary Examiner-Richard L. Moses Attorney, Agent, 0r'Firm--Michael S. Striker [57] ABSTRACT A processing apparatus wherein a dryer follows a first vessel for a supply of developing solution, a second vessel for a fixing bath and a third vessel for a rinse bath. The duct for evacuation of spent gaseous fluid from the dryer contains a heat exchanger whose coil conveys a stream of fresh water which is heated in the coil prior to entering additional heat exchangers in the first two vessels. The additional heat exchangers heat the respective liquids and the last additional heat exchanger discharges heated water into the rinse bath. The 'vessel for developing solution further contains a thermostatically controlled heating unit. The heat exchanger in thedryer receives unheated water from a supply pipe through a valve which is opened in automatic response to admission of films into the first vessel and remains open as long as at least one film trav- 354/319 G03d3/00 89 A 14, 96-,

[73] Assignee: AGFA-Gevaert Aktiengesellschaft,

APPARATUS FOR PROCESSING PHOTQGRAPHIC FILMS [75] Inventors: Erwin Geyken; Gerhard Schwarzmaier; Peter Dawidowitsch, 1.9? Meniehfisma Leverkusen, Germany Sept. 4, 1973 Foreign Application Priority Data Sept. 2, 1972 Germany,........;..................

Field of 95/89 R 6 References Cited UNITED STATESPATENTS United States Patent Geyken et al;

[22] Filed:

[21] Appl. No.: 393,834

[51] Int. Cl.

pta-

930 Hopkins.......................

958 Debrie 960 Hixon et al. Winnek.......

1 APPARATUS FOR PROCESSING PHOTOGRAPHIC BACKGROUND OF THE INVENTION The present invention relates to apparatus for processing photographic films or the like, and more particularly to improvements ,in' processing apparatus wherein successive films or analogous carriers of photosensitive material are conveyed along an elongated path extending seriatim through at least one developing or fixing bath, thereupon through a rinse bath-and finally through a dryer. Still more particularly,the invention relates to improvements in means for heating the liquid or liquids which Contact the films during travel through a processing apparatus. Processing apparatus of the just outlined character are used, for example, in treatment of exposed X-ray films.

A drawback of presently known processing apparatus of the type wherein the films must pass through one or more baths which contain various chemicals and thereupon through a rinse bath anda dryer is that the apparatus must be provided with connections for hot and cold water. The connections for hot and cold water serve to deliver hot and cold water to a thermostatically controlled mixer valve which regulates the temperature of the water stream entering the processing apparatus, for example, the rinsing station. As a rule, the mixer valve is designed to insure that the temperature of water flowing to the rinsing station remains constant or fluctuates negligibly within a narrow range. The mixer valve and the temperature regulating means therefor are expensive and bulky. Moreover, such apparatus can be used only in locations having outlets for cold and hot water.

SUMMARY OF THE. INVENTION An object of the invention is to provide a novel and improved automatic or semiautomatic processing apparatus for X-ray films and/or other types of carriers forphotosensitive material wherein the temperature of liquid agents which come into contact with films can be regulated with a necessary degree of accuracy without resorting to complex, expensive and sensitive thermostatically controlled mixer valves or the like. 7

Another object of the invention'is to provide a processing apparatus for exposed photographic films or the like with novel and improved means for heating at least one of two or more liquid agents which contact the films during transport toward the dryer.

A further object of the invention is to provide a processing apparatus for exposed photographic films wherein the temperature of one or more liquid agents can be regulated with a requisite degree of accuracy evenif the laboratory wherein the apparatus is installed does not have an outlet for hot water.

Anadditional'object of the invention is to provide a novel and improved dryer'for use in a processing appa constructed and assembled in such a way that the temperature of one or more liquid agents therein does not drop appreciably in response to shorter-lasting or even longer-lasting interruptions in the operation of processing apparatus. I 1 l The invention is embodied in a processing apparatus for exposed films or analogous sheetor web-like carriers of photosensitive material. The apparatus comprises a series of vessels each of which contains a supply of a processing liquid (such as a developing solution, a fixer and a rinse bath), a dryer, means for circulating in the dryer a heated gaseous fluid, means for transporting carriers of photosensitive material through successive vessels and thereupon through the drier, a source of unheated liquid (e.g., fresh water), a first heat'exchangerwhich is connectable with the source of unheated liquid and is installed in (and may form part I the first heat exchanger and flows through the additional heat exchanger heats the supply of liquid in the one vessel.

The one vessel may further contain thermostatically controlled heating means. Such heating means may be installed in the vessel for a developing solution whih is circulated in the respective vessel by a pump or the like. The heating means is preferably located downstream of the additional heat exchanger, as considered in the direction of circulation of developing solution.

The additional heat exchanger has an outlet which may discharge heated liquid into the rinse bath.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved processing apparatus itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawing;

BRIEF DESCRIPTION OF THE DRAWING DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a processing apparatus 2 for photographic films l. The leading end of an exposed film 1 which is fed into the processing apparatus 2' is engaged by two advancing rolls 3, 4 which introduce the film into a first vessel or tank 9 containing a holder or rack 5 for several sets of pairwise arranged transporting rollers 6, 7 serving to move the film along a substantially U-shaped path having a downwardly and an upwardly extending section. The tank 9 contains a supply of a developing solution whose upper level is determined by an overflow pipe 10 which is connected with an evacuating pipe 1 l. The tank 9 preferably consists of a synthetic thermoplastic material which is resistant to the .tank 9.

wall of thetank 9 has an outlet 9a which is connected with the intake of a pump 12 serving to circulate developing solution in the tank 9. The outlet of the pump 12 is connected with an inlet 9b in the bottom wall of the A thermostatically controlled heating unit 30 in the bottom portion of the tank 9 serves to maintain the developing solution at a predetermined temperature. The heating unit 30 may comprise one or more rod-like heaters which are preferably adjacent to the inlet 9b in the bottom wall of the tank 9.

The outlet 9a is further connected with the evacuating pipe 11 by means of a conduit 90 which contains a normally closed shutoff valve 13. The valve 13 is opened when the pump 12 is arrested and the operator wishes to evacuate the contents of the tank 9.

The film l which leaves the tank 9 is introduced into a second vessel or tank 14 which is somewhat shallower than the tank 9. The tank 14 contains a rack 8 with sets of pairwisearranged transporting rollers 6, 7 which move the film 1 along a second U-shaped path. The tank 14 contains a supply of a fixing agent or fixer whose level is determined by an overflow pipe a connected to the evacutating pipe 11.

The tank'l4 is followed by a third vessel or tank 15 for a rinse bath. The level of water in the tank 15 is determined by an overflow pipe 10b whichis connected to the evacuating pipe 11. The tank 15 contains a rack 8a with sets of transporting rollers 16, 17 and a guide roller 18whichdirects the film 1 into a dryer 19. The transporting rollers l6, l7 define for the film l a substantially U-shaped path similar to the path defined by the rollers 6, 7 on the rack 8 in the tank 14. The reference characters 12a and 12b denote pumps which respectively serve to circulate fixer and water in the tanks 14 and 15. The contents of the tanks 14 and 15 can be evacuated in response to opening of normally closed shutoff valves 13a, 13b. The dimensions of the tank 15 equal or approximate the dimensions of the tank 14.

The last pair of transporting rollers l6, 17 in the tank 15 serves to remove surplus water from the film l and the guide roller 18 is preferably heated by hot gaseous fluid in the dryer 19. The dryer 19 containsla rack 8b for sets of pairwise arranged transporting rollers 20 which advance the film 1 along an elongated downwardly extending path including one or more arcuate sections. The film which is advanced by the transporting rollers 20 moves counter to'the direction of flow of a stream 21 of hot drying gas, preferably air, and the dried film is allowed to descend into an intercepting receptacle 22 located at the lower end of the dryer 19. The air stream 21 issues from'the outlet of a suitable blower 119 and is heated by a thermostatically controlled heater 219 before it enters the dryer 19, The heated air stream 21 enters the dryer 19 by way of an opening 23 which is adjacent to the receptacle 22 and spent air is evacuated by way of two channels or ducts 24, 25 whose intake ends are adjacent to the upper end of the path along which the film 1 moves through the dryer 19. The discharge ends of the channels 24, 25 are connected to the suction inlet of the blower 119 so that the stream 21 is circulated along a substantially closed path. A certain amount of fresh air is preferably added to the stream 21, for example, at the suction inlet of the blower 119. This insures that the moisture content of corrosive influence'of developing solution. The bottom 1 4 air which forms the stream 21 does not exceed a predetermined maximum value. 1

A heat exchanger 26 (seealso FIG. 2) is installed in the channel 24 to withdraw heat-from the respective ture content.

The intake end of the coil 26b is connected with a supply pipe 27a for fresh water which constitutes a source of unheated liquid. The pipe 27a is connected with the coil 26b by a flow regulating valve 27 which is preferably an electromagnetically operated valve and opens in automatic response to introduction of a film 1 into the inlet of the tank 9. To this end, the processing apparatus 2 comprises a control means including a detector 28 (e.g., a normally open switch) which generates a signal to energize the electromagnet 27d of end to thus open the valve 27 in response to introduction of a film 1 into the nip of the advancing rolls 3, 4. As

I shown, the roll 3 constitutes a follower which is moved away from the roll 4 to thereby close the switch 28 as soon as the leading portion of a film 1 is introduced between the advancing rolls. The arrangement is prefera bly such that the valve 27 remains open for an interval of time which is required to transport a film through the processing apparatus 2. To this end, the conductor means 27b between the detector switch 28 and the electromagnet 27d of the valve 27 contains a timedelay relay 270 or the like which insures that the delay with which the valve 27 closes subsequent to opening of the switch 28 suffices to guarantee that the last film I of a series of films has reached the receptacle 22.

A second heat exchanger (similar to or different from the heat exchanger 26) can be installed in the duct 25 of the dryer 19, and such second heat exchanger can be connected in series or in parallel with the heat exchanger 26. it is further clear that the heat exchanger 26 can be installed in the channel 25. I

The discharge end of the coil 26b is connected to the intake end of a coil forming part of a first additional heat exchanger 29 which is installed in the lower portion of the tank 9. The liquid which issues from the coil of the heat exchanger 29 enters the coil of a second ad- I ditional heat exchanger 31 in the lower portion of the tank 14. The'discharge end of the coil of the heat exchanger 31 admits water into the tank l5.

It will be noted that the transporting rolls 20 move the films l downwardly through a first portion 19a of the dryer 19 wherein the films are contacted by the v ascending stream 21 of hot air, and that the heat exchanger 26 is installed in that portion (duct 24) of the drayer 19 which receives spent air from the portion 19a. This insures that unheated liquid flowing in the coil 26b withdraws heat from the air stream 21 after the air stream has completed the drying of films 1 in the dryer portion 19a.

The operation is as follows:

The cross-sectional area of the passage defined by the valve 27 for the flow of cold water from the, source or pipe 27a into the coil 26b of the heat exchanger 26 is selected in such a way that the pipe27a admits water at a rate which is needed for continuous operation of the processing apparatus 2. For example, when the apparatus 2 is toprocess 400 X-ray films per hour, the valve 27 can be set to admit into the coil 26b cold water at a rate of 2% liters per minute. The thus admitted stream of freshwater flows in the coil 26b and is heated by moist air in the duct 24. As explained above, the coil 265 can discharge preheated water into a similar coil of a second heat exchanger in the duct 25 of the dryer 19. The fins 26a insure a highly satisfactory exchange of heat between water in coil 26!) and air in duct 24. For example, the temperature of air which enters the duct 24 may approximate 45 C. which is well above the temperature of fresh water in pipe 27a. The temperature of water leaving the coil 26b depends on the rate of water flow through the heat exchanger 26; for example, the temperature of such water may be raised to 20 C. or thereabout.

The valve 27 is opened in automatic response to in-' troduction of a film 1 into the nip of the advancing rolls 3, 4 because the roll 3 then closes the switch 28 which energizes the electromagnet 27d of the valve 27. As mentioned before, the relay 27c insures that the valve 27 remains open as long as at least one film 1 travels from the advancing rolls 3, 4 toward the intercepting receptacle 22. Thus, the valve 27 remains open continuously as long as the films 1 are fed at a rate which suffices to insure that a fresh film l isintroduced into the nip of the advancing rolls 3, 4 before the preceding film reaches thereceptacle 22. Eve ntual heating of water in the coil 26b. beyond a preferred average temperature does no harm; on the contrary, heated water in the coil 26b and in the coils of additional heat exchangers 29, 31 then prevents excessive cooling of the processing liquids in the tanks 9, 14 and 15 when the apparatus 2 is at a standstill, for example, between thetreatment of the last film l of a first series and the treatment of the foremost film of the next series.

The temperature of water in the coil 26b and in the coils of additional heat exchangers 29, 31 reaches a desirable optimum value shortly after the valve 27 opens. The waterremains at such optimum temperature regardless of whether the apparatus 2 is used intermittently or continuously. As mentioned above, eventual slight overheating of water in the heat exchangers'does no harm and is even useful because slightly overheated water prevents an abrupt cooling of processing liquids in the tanks 9, l4 and 15. lf the moisture content of hot air which leaves the dryer 19 through the duct 24 is very high, and especially if the flow of waterin the coil 26b is counter to the direction of air flowin the duct 24, the external surface of the coil 26b and the exposed surfaces of the fins 26a are likely to be coated with condensate. This is desirable when the duct 24 does not discharge spent air into the atmosphere, i.e., when the outlet of the duct 24 is connected to the inlet of the blower 119 which admits'the. air stream 21 into the dryer 19 through the opening 23. Thus, the accumulation of condensate on parts of the heat exchanger 26 reduces the moisture content of air which flows in the duct 24. The condensate can be evacuated at the colder (intake) end of the coil 26b.

The difference between the temperature of water which leaves the coil 26b and the temperature of developing solution in the tank 9 is normally slight, e.g., in the range of a few degrees C. If the heat exchanger 29 is placed close to the outlet 9a of the tank 9, such small difference (in the range of one or more degrees C.) suffices to insure that water flowing in the coil of the heat exchanger 29 maintains the developing solution which flows into the pump 12 at a temperature which is constant or substantially constant, i.e.,'which differs from the desired optimum temperature of developing solution in the tank 9 by a substantially constant value. If

the heating unit 30 is placed upstream of the heat exchanger 29, as considered in the direction of circulation of developing solution in the tank 9, the heating unit 30 can raise the temperature of liquid entering via inlet 9b to the optimum temperature for treatment of films in the tank 9. It has been found that the heating unit 30 can be controlled with such a high degree of accuracy that the temperature of developing solution fluctuates negligibly and is normally within one or more tenths of 1 degree C. of'the desired optimum tempera-- ture.

The temperature of water which flows in the coil of the heat exchanger 31 is only slightly less than the temperature of developing solution in the tank 9. Consequently, the heat exchanger 31 can raise the temperature of fixing bath in the tank 14 well above room temperature and such temperature is only slightly less than the temperature of liquid in the tank 9. The fixing bath in the tank 14 is further heated owing to exchange of heat with developing solution through the wall which separates the tanks 9 and 14. Such dual exchange of heat normally suffices to maintain the temperature of liquid in the tank 14 within a narrow range without resorting to additional temperature regulating devices.

The discharge end of the coil in the heat exchanger 31 communicates with the rinse bath in tank 15. This insures that the temperature of liquid in the tank 15 is well above room temperature and is not appreciably below the temperature of developing solution in the tank 9. It has been found that such heating of rinse bath insures a highly satisfactory rinsing of films 1 in spite of the fact that the amounts of circulated water in the tank 15 are relatively small. For example, the pumps 12, 12a and 12b can be designed to circulate the respective liquids at the rate of 22 liters per minute. The rate of outflow of chemicals-containing water via pipe 11 equals the; rate of admission of fresh water through the valve 27.

The processing apparatus 2 need not be connected to a hot water supply line and need not employ any valves for the mixing of hot and cold water. The operation is satisfactory regardless of whether the films 1 are fed continuously or intermittently.

It is clear that the developing apparatus can be modified in a number ofjways without departing from the spirit of the invention. For example, the heat exchanger 31 in the tank 14 can be omitted. Also, the heat exchanger 26 can be connected with the heat exchanger 31 and the heat exchanger 29 omitted if the heating unit 30 is capable of maintaining the temperature of developing solution in tank 9 within a desired range. The heating unit 30 can be omitted if the heat exchanger 29 is capable of preventing excessive fluctuations of liquid temperature in tank 9 above or below an optimum temperature. For example, the heating unit 30 or the heat exchanger 29 will be omitted if the nature of films and- /or the natureof developing solution is such that the temperature of liquid in the tank 9 can fluctuate within 1 or more degrees C.

The heat exchanger 26 constitutes but one form of means for withdrawing heat from gaseous fluid which leaves the dryer 19. For example, the frame of the dryer 19 can be assembled of pipes which are welded together and form one or more coils for fresh water. Also, the rack 86 and/or other parts (e.g., a heatinsulating jacket) of the dryer 19 can be provided with internal compartments for circulation of fresh water which is thereby heated prior to exchanging heat with liquid in the tank 9, 14' and/or 15. The rack 8b and/or the frame of the dryer 19 may be made hollow and can receive one or more, heating coils for fresh water. As a rule, heat can be withdrawn from all such parts which are heated automatically when the processing apparatus is in use.

An important advantage of the heat exchanger 26 is that the stream of water entering the heat exchanger 29 is heated well above the temperature of fresh water in the pipe 270. As mentioned before, the temperature of water leaving the coil 26b is normally only a few degrees C. below the desired optimum temperature of developing solution in the tank 9. This insures that the heat exchanger 29 withdraws from developing solution only such quantities of heat as are necessary to insure that the heating unit 30 can maintain the developing solution at the optimum temperature. Moreover, the liquid which leaves the heat exchanger 31 is sufficiently hot to insure an optimum heating of the rinse bath.

The detector 28 and relay 270 for the valve 27 can be replaced with other types of control means for regulating the rate of admission of fresh water in dependency on the number orcombined surface area of films which are transported from the advancing rolls 3, 4 toward the receptacle 22. For example, such regulation can be effected by resorting to a control system of the type disclosed in German Pat. No. 1,237,789 which describes a pulse storing unit serving to receive and store a number of pulses and to erase the pulses at given intervals. Such storing unit can be used to control the valve 27 by receiving a number of pulses each of which corresponds to a film. of a series of films'to be treated, by maintaining the valve 27 in open position during erasure of successive pulses while the films pass through the tanks 9, l4, l and dryerl9, and by closing the valve 27 upon completion of treatment of the last film.

Without further analysis, the foregoing will so fully. reveal the gist of the present invention that others-can,

by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of our contribution to the art and,

' therefore, such adaptations should and are intended to.

fluid; means for transporting carriers of photosensitive material through successive vessels of said series and thereupon through said dryer; a source of unheated liquid; a first heat exchanger connectable with said source and installed in said dryer so that unheated liquid which is supplied by said source is heated in said heat exchanger; and at least one additional heat exchanger connected with said first heat exchanger and arranged to circulate heated liquid in one of said vessels so that heated liquid supplied by said first heat exchanger and flowing in said additional heat exchanger heats the supply of liquid in said one vessel.

2. A combination as defined in claim 1, further comprising thermostatically controlled heating means provided in and arranged to heat the supply of liquid in at least one of said vessels.

3. A combination as defined in claim 1, wherein said unheated liquid is fresh water and the supply of liquid in another of said vessels is a'rinse bath, said additional heat exchanger having an outlet arranged to discharge heated water into said rinse bath.

.4. A combination as defined in claim 1, wherein said dryer comprises a first portion and a second portion located downstream of said first portion, as considered in the direction of circulation of gaseous fluid in said dryer, said means for transporting being arranged to transport carriers of photosensitve material through said first portion and said firstheat exchanger being arranged to effect an exchanger of heat between unheated liquid and the gaseous fluid in said second portion of said dryer.

5. A combination as defined in claim 4, wherein said second portion of said dryer is a duct wherein said gaseous fluid flows on its way from said dryer.

6. A combination as defined in claim 1, wherein said first heat exchanger comprises a coil for unheated liquid and heat exchanging fins surrounding said coil.

7. A combination as defined in claim 1, wherein said dryer comprises a frame and said first heat exchanger forms part of said frame.

8. A combination as defined in claim 1, wherein said dryer comprises a jacket and said first heat exchanger v forms part of said jacket.

9. A combination as defined in claim 1, further comprising means for circulating the processing liquid in said one vessel and thermostatically controlled heating means for processing liquid in said one vessel, said additional heat exchanger being located upstream of said heating means as considered in the direction of circulation of processing liquid in said one vessel.

10. A combination as defined in claim 1, further comprising valve means installed between said first heat exchanger and said source of unheated liquid and control means for maintaining said valve means in open position while at least one of said vessels or said dryer contains at least one carrier of photosensitive material.

vessel of said series of vessels.

vice. 

1. In a processing apparatus for exposed films or analogous sheet- or web-like carriers of photosensitive material, a combination comprising a series of vessels each containing a supply of a processing liquid; a dryer; means for circulating in said dryer a heated gaseous fluid; means for transporting carriers of photosensitive material through successive vessels of said series and thereupon through said dryer; a source of unheated liquid; a first heat exchanger connectable with said source and installed in said dryer so that unheated liquid which is supplied by said source is heated in said heat exchanger; and at least one additional heat exchanger connected with said first heat exchanger and arranged to circulate heated liquid in one of said vessels so that heated liquid supplied by said first heat exchanger and flowing in said additional heat exchanger heats the supply of liquid in said one vessel.
 2. A combination as defined in claim 1, further comprising thermostatically controlled heating means provided in and arranged to heat the supply of liquid in at least one of said vessels.
 3. A combination as defined in claim 1, wherein said unheated liquid is fresh water and the supply of liquid in another of said vessels is a rinse bath, said additional heat exchanger having an outlet arranged to discharge heated water into said rinse bath.
 4. A combination as defined in claim 1, wherein said dryer comprises a first portion and a second portion located downstream of said first portion, as considered in the direction of circulation of gaseous fluid in said dryer, said means for transporting being arranged to transport carriers of photosensitve material through said first portion and said first heat exchanger being arranged to effect an exchanger of heat between unheated liquid and the gaseous fluid in said second portion of said dryer.
 5. A combination as defined in claim 4, wherein said second portion of said dryer is a duct wherein said gaseous fluid flows on its way from said dryer.
 6. A combination as defined in claim 1, wherein said first heat exchanger comprises a coil for unheated liquid and heat exchanging fins surrounding said coil.
 7. A combination as defined in claim 1, wherein said dryer comprises a frame and said first heat exchanger forms parT of said frame.
 8. A combination as defined in claim 1, wherein said dryer comprises a jacket and said first heat exchanger forms part of said jacket.
 9. A combination as defined in claim 1, further comprising means for circulating the processing liquid in said one vessel and thermostatically controlled heating means for processing liquid in said one vessel, said additional heat exchanger being located upstream of said heating means as considered in the direction of circulation of processing liquid in said one vessel.
 10. A combination as defined in claim 1, further comprising valve means installed between said first heat exchanger and said source of unheated liquid and control means for maintaining said valve means in open position while at least one of said vessels or said dryer contains at least one carrier of photosensitive material.
 11. A combination as defined in claim 10, wherein said control means comprises detector means arranged to monitor the admission of carriers into the foremost vessel of said series of vessels.
 12. A combination as defined in claim 11, wherein said valve means comprises electromagnet means which is energized in the open position of said valve means and said detector means comprises means for energizing said electromagnet means.
 13. A combination as defined in claim 10, wherein said control means comprises an impulse storing device. 